LTE-A (Long Term Evolution-Advanced, LTE-Advanced) is the advancement of a broadband radio communication technology standard 3GPP LTE which is closely concerned currently. In order to improve a throughput at an edge of a cell, a relay node (Relay Node, RN) is introduced into the LTE-A, so as to facilitate temporary network deployment demands for operators or users, and support a group movement function, where the RN may be deployed at rural, urban, and an indoor hot spot region or a blind spot region.
The RN is located between a Donor eNB (DeNB, Donor eNB) to which the RN belongs and a UE, the RN sends a downlink signal to the UE, or sends an uplink signal to the DeNB, where an air interface between the RN and the DeNB is called a Un interface, and an air interface between the RN and the UE is called a Uu interface. Data from the DeNB to the UE passes through two segments of air interfaces, that is, the data reaches the UE through two hops. As more RNs are added, a multi-hop scenario may also occur in the LTE-A.
Due to the introduction of the RN, the segment number of air interface links is increased, a key level is also increased, and an existing security mechanism is incapable of performing effective security protection on data on each segment of an air interface.